linux-kernel - Re: BUG: gpio: pca953x: 24 bit expanders broken since v5.2-rc1

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Message-ID: <CACRpkdajVu2H-9zX4gAEnHHR8gd=4jseabLGsHB=0CF1BKH-JA@mail.gmail.com>
Date:   Sat, 1 Jun 2019 23:57:46 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     "H. Nikolaus Schaller" <hns@...delico.com>
Cc:     Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Nandor Han <nandor.han@...sala.com>,
        Mark Brown <broonie@...nel.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Tony Lindgren <tony@...mide.com>,
        Discussions about the Letux Kernel 
        <letux-kernel@...nphoenux.org>, kernel@...a-handheld.com,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: BUG: gpio: pca953x: 24 bit expanders broken since v5.2-rc1

On Fri, May 31, 2019 at 7:06 PM H. Nikolaus Schaller <hns@...delico.com> wrote:

> Now, this was not a (visible) problem until patch
>
>         8b9f9d4dc511 regmap: verify if register is writeable before writing operations
>
> enforces to check the register number before invoking the
> callback pca953x_writeable_register(). pca953x_writeable_register()
> seems to know about REG_ADDR_AI (through reg & REG_ADDR_MASK) and
> accepts 0x88 as a valid register number.
>
> After the regmap patch the register is checked against
> pca953x_i2c_regmap.max_register before applying REG_ADDR_MASK
> and 0x88 is obviously beyond, explaining the symptom.

Can we simply bump the .max_register in
pca953x_i2c_regmap to 0xff for a quick fix with a comment
FIXME to figure it out the right way?

Yours,
Linus Walleij